Nuclear reactor fuel paste composition



E3315; 9;, 1 9651 R; DICKINSON; EEAL. 3,169,117

NUCLEAR; REAcTom PASTE? comeosmrow 5 Sheets-Sheet I ROBERT W. DICKINSON BY DONALD T. EGGEN /24 L. w \WIIIIHHHMA Eiledi v 1961 ATTORNEY Feb. 9, 1965 R. w. DICKINSON ETAL 3,169,117

NUCLEAR REACTOR FUEL PASTE COMPOSITION 5 Sheets-Sheet 2 Filed May 9, 1961 INVENTORS ROBERT W. DICKINSON BY DONALD T. EGGEN Q/JMMJ- V4.

ATTORNEY Feb. 9, 1965 R. W. DICKINSON ETAL NUCLEAR REACTOR FUEL PASTE COMPOSITION Filed May 9, 1961 COOLANT TUBE INSIDE DIAMETER (in) 5 Sheets-Sheet 3 CORE DIAMETER OR HEIGHT (f?) FIG. 3

FIG. 6

9 INVENTORS ROBERT w. DICKINSON BY DONALD T. EGGEN ATTORNE 1 965 LR.I2DICKINSON ET-AL 3,169,117

momma REACYEOR =FUEL mswE .COMBGSLTION :5 Sheets-Sheet 4 iF'i'led May 9', 1961 O 8 6 4 2 l l I CORE HEIGHT OR DIAMETER (ft) INVENTORS ROBERT w. DICKINSON y DONALD T. EGGEN ATTORNEY Feb. 9, 1965 R. w. DICKINSON ETAL 3,159,117

NUCLEAR REACTOR FUEL PASTE COMPOSITION 5 Sheets-Sheet 5 Filed May 9, 1961 s a l 0 o CORE HEIGHT OR DIAMETER (ft) FIG.

INVENTORS ROBERT W. DICKINSON By DONALD T. EGGEN ATTORNEY structure.

i v 3,159,117 NUCLEAR nsacron FUEL PASTE coivirosirrow 7 Robert W. Dickinson, Northridge, and Donald T. Eggen,

Santa Susana, Califi, assignors, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Filed May 9, 1961, Ser. No. 108,880 3 Claims. (Cl. 252-6011) The present invention .is directed to nuclear reactors and more particularly to a paste-fueled fast reactor.

The feasibility of afast breeder power reactor has been established thy-the Experimental Breeder Reactor I. In

such a reactorthe greatest potential for economic improvement lies in the areas of increased achievable burnup and reduced fabrication and processing costs.

The prior art reactors of this typevutilize solid fuels, which limit theoperating .centerline temperature to the order of 400 C. and which result inlow specific powers. Further, where centerline temperatures in the moredesirable range of 609 to 750 C. have been tried whileattempting to achieve high burnup, i.e., two percent, distortion and swelling of the fuel has resulted. This distortion problem associated with solid fuels is? apparently due to the retention of fission gases and products within the solid The present invention has as its primary purpose the utilization of .a paste fuel ina nuclear reactor, thereby avoiding the growth and distortion problems associated with solid-fueled-reactors. l Another. object of the present invention is to provide 3,16%,117 Patented Feb. 9, 1965 lCe.

plugs 32. Control elements 33 are suspended the top shield for insertion into the 'core 34; Within the reactor vessel 22 is a thermal shield 36 extending around and spaced from the centrally located core 34. Coolant inlets 33 and outlets 4% are provided in the vessel 22, the

inlet 38 being connected to an inlet plenum 42. The

inlet plenum 42 is separated from the remainder of the reactor vessel 22 by a grid plate 44, supported by a plurality of supports 46, and has a plurality of apertures in which the fuel elements 43 are placed. The core is comprised of a plurality of closely packed hexagonal fuel elements 43 which form a right cylinder. A radial and axial. blanket region Sil made up of similarly shaped elements surrounds the core. The blanket elements contain a paste composition containing fertile material.

' Radially outward from the core 34 and blanket 59 is a canned graphite reflector 52, and a storage space 54 a nuclear reactor with increased specific power and increased burnup capability.

'Another object of the present invention is to provide a nuclear reactor in which the fuel is in paste form and. is either confined within a fuel container or is mobile through the reactor core so that fission gases and products may be removed from the active portion of the core.

' A further object of the presentinvention is the elimination of the costly and: complex operations associated with solid fuel elements previously utilized in fast reactors of decladding and reconstitution of fissionable-and fertile material. V a H These and other objects and advantages of the present invention will be more apparentfrorn the following'del tailed description'and drawings, madea part hereoffin' which: v ,7

FIGURE 1 is a partially sectioned perspective View of one embodiment of the reactor of the present inyfi'n tion;

FIGURE 2 the fuel element utilized inthe embodiment of FIG- URE l; I

FIGURE 3 is a schematic view of another embodiment of the present invention; a 1 i Y 1 FIGURE 4 is a graph of core enrichment gvsgcore diameter;

FIGURES is a core diameter; and

graph of initial conversion ratio vs. -FIGURE 6 is. a graph coo l antgtube inside'diameter vs. core diameter.

Referring now'to the drawings in detail, one embodim'ent' of the paste-fueled, fast reactorofthe present in-- vention is shown in FIG. land includes an outer'vessel V 20 in 'which'a sealed reactor vessel 22 is positioned, both vessels 2t) and 22 being sealed to the containmentvessel 24 by bellows '26 to allow independent*expansion and contraction. A-top shield plug 28 is centrally located above the reactor-yessel-22and has the conventional center plug 30 and fuel and blanket element removal for fuel elements.

The core and blanket elements are shown in FIG. 2 and are composed of a hexagonalshell 60, an upper and lower tubesheet 62 and 64, respectively, and a plurality of tubes 66. The tube sheets 62 and 64 are welded or otherwise sealed to the shell and have a plurality of apertures in which the tubes 66 are sealed. In this manner a sealed chamber 68 is provided within the shell 66 which is traversed by a plurality of tubes 66. Within 7 the sealed chamber 68 a quantity of static paste fuel 70 is placed. A coolant inlet header 72 is connected to the bottom of shell 60 and fits into the apertures of grid p1ate'44 so that the liquid metal coolant is directed upwardly through the tubes 66 into the coolant outlet header .74- and then through holes 75into the liquid metal pool '76fabove the reactorcore. -A gas space 77 provides for paste fuel thermal expansion and for fission gas release accumulation.

A hold-down mechanism, not shown, located above the core prevents axial movement of the fuel elements from the force of sodium flow and provides lateral support.

Referring now to FIG. 3, a second embodiment of the present invention is shown andincludes a reactor vessel .86 containing'a quantity of fertile (blanket) material in liquid form,.i.e., U 5 or "H1 in a liquid metal. The

- vessel 80 has an inert g as 82 above itstop level'84 and a conventional top shield plug, not shown; Supported within the vesselv sil-a-ndbelow the level 84 is a core 85 con: sistingof a top plenum 8 6 communicating with the interiorof a plurality of tubes 87 which are connected at is apartially sectioned perspective view of their lower extremity to an outlet plenum 88; The plenurn86 is connected to a source of paste fuel by pipe 89, whilethe outlet plenum 88 is connected through pipe to-a fuelreproccssing system and/or to the source of paste fuel, The paste fuel is pumped by pump 91, either continuouslyor discontinuously, through the tubes'ti'l'. The

plas-te fuel in the tubes 87 and inletand outletplenums .86. and 88 constitutes a critical mass ofl-fissionable fuel.

The pipes 89 and 90 are so constructed that a critical amass. is not present,-i.e., the' diameter is suificiently small that a critical mass is notcapableof being present re-- gardless of. the length. QAdditionally, neutron absorbers may be utilized asan added safety precaution. .The core 85 is cooled by a crossfiowing coolant which is pumped by pump 93 through the inlet pipe 92 to the -'coolant inlet plenum 94 andthrough the core 85' along I the outside of the tubes .87 containing the fuel. The heated sodium then passes through coolant outlet plenum 96 and outlet pipe 98 to a conventional heat'utilization' system." In this manner the paste fuel may be slowly rndvedlthroughQthe critical volume while the heat is con:

tinuoiisly extracted. It is alsob contemplated by the pres-3- en-t'invention to pump the paste in surges so'that only a portion of the core fuel materialis replaced with new fissionable material during a specified period or time. This embodiment preferably includes-a reflectorexternal to the vessel 30. I I

In the present invention, paste fuels are defined as small, solid, spheroidal particles (approximately 100 inieron diameter) of fissionaole and fertile alloys or compounds, packed to a settled density of about 4-0-60 vol- "fume percent with the interstices between the particles -filled with liquid metal. Such settled two-phase systems are pastes, as distinguished from slurries that are twolphase systems in which the particles are dispersed (susi-pended) in the liquid by constant agitation. [See also fi iammitt et al., The Fission Gas Problem for vMobile :Fuel Fast Reactors, Nuclear Science and Engineering 7:

In contrast to most of the mobile-fuel reactor concepts, the past reactor of the embodiments in FIGS. 1 and 3 does not use the fuel to transport heat from the reactor. The fuel in the embodiment of FIG. 3 is moved-at a low velocity and in relatively small volumes through the reactor. The low velocity of the pastes substantially elimif nates problems of erosion of containers by the particles and particle breakdown by attrition. By utilizing a noncorrosive liquid metal, le.g.,.sodium,'in which the fuel material is insoluble, both corrosion of containers and mass transport are minimized. Such a system has the advantages of increased resistance of fuel to irradiation damage anddimensional change, ease of fuel fabrication, simplification of reactor loading, and unloading (at full power), integrated reprocessing and refabrication, and simplification of non-fuel portions of the reaction system.

The fuel materials utilized in the embodimen'tsof the present-invention are UC, PuC, ThC-UC, ThC- PuC, and I FuC-UC. The high thermal conductivity of UC results in a high heat transfer rate. Sodium is preferred as the liquid metal carrcr as Well as the coolant, although lead tion materials at thefpreferred temperatures introduces significant problems of construction and maintenance.

FIGURE 4 shows-the relationship between core enrichrnen-t and criticalmass for a paste-fueled, sodiumcooled fast reactor where the enrichment is defined as the atom fraction of U in U or Pu in U plus Pu. These relationships are based upon a k f of 1.050 with a peak fuel temperature of 1600 F., a pastefertile material of U Cand ablanket and refieetorthiclmess ofi18 inches I each. Curve is for the UC paste fuel casein a sodium carrier, while curve i'lll is for the PuC-UCcase, both curves showing the core enrichment (a/o) (left scale) as a function of core diameter or height. Curve 102 shows the relationship of the core height or diameter asa function of the core c'ritical massiright-hand scale). FIG. 5 shows the relationship between initial conversion ratio as a function of core height or'diameter for the V caSe'ofUG (curve 103) and for PuC-UC (curve 104);

these two curves are derived upon'the same basesas curves 100-102. I I

FIGURE 6 shows thevariation in jcore diameter or height as a functionbfcoolant" tube inside'jdiametcr. Curve 105 is based-upon a total power of 704 mwt. with a maximum fuel temperature of 1600 F.I

."With these relationships the characteristics of a number of paste-fueled fast reactors are shown in the "follow- Table II and covers the case. of a PuC-UC fuel in a sodium carrier as a paste fuel. p

gable I B. Sodium outlet temperature F.) 1200 t C. Sodiuminiet temperaturei F.) l 650 D. Sodium flowrate (lb/hr.) 14.5 10 E. Peak fuel temperature F.) 1600 F. Fast region volume fractions:

(1) Fuel e e- 0.20 (2) Sodium carrier 0.20 ('3) Sodium coolant 0.45 (4) 'Stainless steel 0.15 G. Blanket region volume fractions:

(1) Fertile material 0.40 (2) Sodium 0.49 (3) Stainless steel 0.11 H. Reflector region volume fractions: I

(1) Graphite 0.97 i (2) Sodium 0.025 (3) Stainless steel 0.005

Table II.UC-Na FAST REGION A. Fuel no I no B. Dimensions:

1'. Core Diameter (it) 5.0 7.0 2. Tube'LD. (in.) 0.340 0.55. 3. Tube Wall Thickness (in.) 0.017 0.0275

0. Nuclear: V

1. Power (Percent of total) 97. 4 08. 5 2. Enrichment (at. percent U or Pu Yu c 19. 2 14. 2 3. h [ass of Fuel (kg) 7,450 20,4 0 4. Mass of U (kg)- 1, 415 3, 730 5. Mass 0iPu +Pul (kg). 0 0 6. Initial Conversion Ratio..." 0.430 0.605 7. Radial Peak-to-Average Powcr .1. 57 1. 70 I 8. Median Fission Energy (kev.) 06 43 I D. Heat Transfer: I I

1. Ptiill; Heat; Fluxon Tub .O.D. (B.t;.u./ 030x10 0.535X10 l.-ft. I. I 2. Average Power Density (kw/ t5} re v gion) I A .4..- 6,970 2,570 3. Average. Specific Power vJkg. W

or Pn'- +Pu2 485 254 4. Average Sodium Velocity (ft./sec.) 8.5 4.4 5. Maximum Sodium Velocity (fl; ./scc.) 13. l 7.4

BLANKET REGION A1 Fertile Material U C U? C B. Region O.D. Dimensions-(17.); i 8.0 10.0 C. Nuclear: v

1. Power (percent of total)---" 2.6 1.5 2. Enrichment".- .00 0.00 3. Mass of FertileMaterial (k 23, 250- 60.800 4. Initial Conversion Ration". 0.375 0.265

D. Heat Transfer; I

.1. Average Power Density '(lrwJit region) I 38 2,'Average Specific Power (kw. 0.70 0. 17 Reflector OJD. Dimensions (ft.) 11 13 Total Reactor Initial Conversion Rat 0. 805 0.870

Table HI PuC-UC-Na rasi" REGION A. Fuel ruo uc PuC-UC B. Dimensions: I

1. Core Diameter (ft-.). 3.0 5.0 2. Tube LD. (in.) a 0. 165 0. 340 3. Tube Wall Thickness (in.) I 0. 00825 0:017 G. Nuclear: v 1. Power (percent of total) 05. 5 97. 4 2. Enrichment (at. percent, U 5 01 Pu 23.3 12.3 3. 1, 630 7, 784 4. 0 Q 5. Mass of Pn +1u (k 392 .250 6. Initial Conversion*Ratio 0. 334 0. :18 7. Radial Peak-.to-Averagc Power 1. 3S 1. 5g 8. MedianFission Energy (he /2)..- v 107 8a D. Heat; Transfer: I I

1. Peak Heat Flux 011 Tube O.D. (B.t.u.l a

nhL-ftfl); 1A5 l0 080x 2. Average Power Density (kwJit.

' region) 31,600 6,900 3. Average SpecificPowcr (km/kg. U i 2 or Pu -FEW) .Q. 172 11.8 4 Average Sodium Velocity (it./sec.) V 5 5. Maximum Sodium Velocity (lt./sec.) II 31. 2 1o. 1

Table IIIContinued BLANKET REGION These characteristics are essentially unchanged for the embodiment of FIG. 3 except that the total fuel inventory would be increased for the external paste pumping and reprocessing systems. In this embodiment less than about percent of the in-core inventory is pumped through the core each day, and preferably about 5 percent every 24 hours.

Although particular embodiments of the present inven tion have been described, various modifications will be apparent to those skilled in the art. Therefore, the present invention is not limited to the specific embodiments disclosed but only by the appended claims.

We claim:

1. A nuclear reactor fuel in paste form comprising a liquid metal and at least one fissionable fuel composition selected from the class consisting of UC, PuC and ThC, said paste containing solid particles of said fuel composition packed to a density of from about 40 to about 60 volume percent of said paste.

2. A nuclear reactor fuel paste composition consisting essentially of a sodium carrier and at least one fissionable fuel in solid particle form selected from the class consisting of UC, PuC and ThC, said solid particles being present in said composition in an amount of from about to about volume percent of said composition.

3. A nuclear reactor fuel composition consisting essentially of a sodium carrier and a fissionable fuel in solid particle form selected from the class consisting of UC, PuC, ThC-UC and PuC-UC, said solid particles having a diameter of about microns and being present in said composition in an amount of from about 40 to about 60 volume percent of said composition.

References Cited by the Examiner UNITED STATES PATENTS 2,910,417 10/59 Teitel 204 FOREIGN PATENTS 790,688 2/58 Great Britain.

OTHER REFERENCES Nucleonics, July 1954, vol. 12, N0. 7, pp. 14 and 15. Atomics, February 1957, pp. 41-45.

REUBEN EPSTEIN, Acting Primary Examiner.

ROGER L. CAMPBELL, CARL D. QUARFORTH,

Examiners. 

1. A NUCLEAR REACTOR FUEL IN PASTE FORM COMPRISING A LIQUID METAL AND AT LEAST ONE FISSIONABLE FUEL COMPOSITION SELECTED FROM THE CLASS CONSISTING OF UC, PUC AND THC, SAID PASTE CONTAINING SOLID PARTICLES OF SAID FUEL COMPOSITION PACKED TO A DENSITY OF FROM ABOUT 40 TO ABOUT 60 VOLUME PERCENT OF SAID PASTE. 